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Conjugation-Length Dependence of Spin-Dependent Exciton Formation Rates in Pi-Conjugated Oligomers and Polymers

M. Wohlgenannt·X. M. Jiang·Z. V. Vardeny·R. A. J. Janssen
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Abstract

We have measured the ratio, r = $σ_S/σ_T$ of the formation cross section, $σ$ of singlet ($σ_S$) and triplet ($σ_T$) excitons from oppositely charged polarons in a large variety of $π$-conjugated oligomer and polymer films, using the photoinduced absorption and optically detected magnetic resonance spectroscopies. The ratio r is directly related to the singlet exciton yield, which in turn determines the maximum electroluminescence quantum efficiency in organic light emitting diodes (OLED). We discovered that r increases with the conjugation length, CL; in fact a universal dependence exists in which $r^{-1}$ depends linearly on $CL^{-1}$, irrespective of the chain backbone structure. These results indicate that $π$-conjugated polymers have a clear advantage over small molecules in OLED applications.

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M. Wohlgenannt, X. M. Jiang, Z. V. Vardeny, R. A. J. Janssen. 2001-12-29. Conjugation-Length Dependence of Spin-Dependent Exciton Formation Rates in Pi-Conjugated Oligomers and Polymers. https://doi.org/10.1103/physrevlett.88.197401

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